<table align="center"  border="1" width="80%">
  <thead>
    <tr>
      <th colspan="2">Table Heading</th>
    </tr>
  </thead>

  <tbody>
<?php

for($i=1 ; $i<=15 ; $i++) {

$color = $i % 3 == 0 ? 'yellow':'lightgreen';

?>
    <tr>
      <td style="background:<?=$color?>" width="10%"><?=$i?></td>
      <td style="background:<?=$color?>">Table Data</td>
    </tr>
<?php }?>
  </tbody>

</table>
